In the present day integrated circuit technology, metallized ceramic modules are provided which are pluggable into printed circuit cards and boards. These modules take the form of a ceramic substrate base having a printed circuit pattern on a surface thereof to which is solder bonded one or more silicon chips. A module cap or cover is employed to provide a hermetic seal. These chips have embedded therein circuits, such as memory driver and sense circuits, operational amplifiers and support logic for these circuits. The circuit chips perform the special electronic functions for the machines they are used with and the chips produce large quantities of heat during their operation. The problem of adequately dissipating this heat is of major concern.
It has been well known to provide heat transfer means or heat sinks for integrated circuit modules. Such means have taken the form, for example, of piston contact between the chip device and a suitable cold plate; the use of cooling fins; the use of an air stream or conductors of liquid coolant; and filling the gap between the chip device and the module cap with a thermal grease or conductive powder or liquid metal.
The aforementioned heat transfer means usually occupy a large amount of space and employ rather critical material. Also, they are relatively expensive to manufacture and are large and heavy in use.
More recently, two relatively new techniques have been involved in the cooling of circuit elements which employ the principles of a thermosiphon and a heat pipe. In the thermosiphon, a container is provided with liquid coolant in an evaporator section and heat input to this section results in vapor which condenses in a condenser section where heat is rejected. The siphon relies on external forces, such as gravity, to return the condensate vertically along the side walls to the evaporator section. As a result, the thermosiphon is a unidirectional heat transfer device (a thermal diode) limited by orientation. The heat pipe also employs a container having liquid coolant in an evaporator section and heat input to this section results in the formation of vapor which condenses in a condenser section where heat is rejected. The heat pipe uses the capillary forces of an internal wick structure to recirculate condensate to the evaporator section. The heat pipe is a relatively expensive heat transfer device due to the cost of the internal wick structure and this is particularly true where a flexible bellows type container is used. A flexible bellows type heat transfer device is preferred for integrated circuit module applications because it provides a secondary flexible heat transfer path which will minimize the force exerted on the chip and solder joints which arise due to tolerance buildup on the chip, substrate, and cap assembly. It became evident that the desirable heat transfer device would be one of the bellows type which would be independent of external forces and which does not require an additional internal wick structure for continuous operation.